1. Field of the Invention
The present invention relates to a method of manufacturing a display screen having a color filter, which is used in a cathode ray tube, a liquid crystal display element or the like.
2. Description of the Related Art
Conventionally, a filter pattern which is made by patterning a pigment layer into a predetermined pattern, is used in various fields. A color filter used in a liquid crystal display apparatus is a typical example of the filter pattern.
Further, as disclosed in, for example, U.S. Pat. No. 2,959,484 or 3,114,065, which is directed to a color cathode ray tube, a phosphor film with an optical filter which has a structure in which an optical filter of a color which corresponding to the color emitted by a phosphor film is provided in a front side of the phosphor film, that is, between the inner surface of the face plate of the panel and the phosphor film, is known. Usually, a plurality of phosphor films having emitting colors of red, blue and green are formed in a dot manner or a stripe manner on the inner surface of the face plate of a color cathode ray tube. As electron beams collide with these phosphor films, the phosphor films emit light, thus displaying an image. A filter-applied phosphor film is designed to achieve an improvement of image display characteristics such as contrast and color purity, and has a structure in which a filter pattern which transmits a light beam of the same color as the color emitted from the phosphor film itself, is provided between the face plate and the phosphor film. With this structure, of the external light made incident, the green and blue components can be absorbed by a red pigment film, the green and red components can be absorbed by a blue pigment film, and the blue and red components can be absorbed by a green pigment film. With use of filter-applied phosphor films, the contrast and the color purity of the display apparatus can be enhanced. For the formation of such a filter film, generally, a pigment film is applied on a substrate, and then an exposure and development are carried out on the film for patterning. During the patterning, a portion of the pigment film, which should remain as a desired pattern is required to have a sufficient adhesion property with respect to the substrate, whereas the other portion is required to have a sufficient removal property. Further, the pigment film is required to have a transparence, and it is required that pigment particles are dispersed uniformly without being gathered irregularly.
However, the bond between pigment particles and that between the pigment and the substrate are, in practice, relatively strong, and therefore some excessive portions of the pigment film are, in many cases, not removed in the development step, but remain on the substrate as residues. In order to avoid this, the following attempt was made. That is, the development was carried out before the pigment film was dried. However, this attempt entails another problem in which a good patterning cannot be carried out. That is, a sharp-edged pattern cannot be obtained. In other words, the boundary between the portion to remain and the portion to be removed after an exposure cannot be formed sharp.
In the case where such a filter is applied between a phosphor film and a substrate, first, a filter film is patterned as the exposure and development are repeated for each color by means of a slurry method. Then, on the filter film thus obtained, a phosphor which emit the same color as that of the filter film is patterned, as the exposure and development are repeated for each color by the slurry method. Thus, the above case involves a great number of production steps, making it complicated.
Under such circumstances, a method in which a phosphor film is applied on a pigment film, and patterning of these two layers is carried out by one exposure, is conventionally proposed (Jap. Pat. Appln. KOKAI Publication No. 52-77578 or No. 5-266795).
However, in the above-described method in which the patterning of the phosphor layer and the pigment layer is carried out by only one exposure, the phenomenon that the first film is dissolved while the second film is applied, easily occur. If the first layer is completely hardened in order to avoid the above drawback, the first film cannot be easily dissolved and removed by the development, which is carried out after the formation of the second layer. As a result, it is difficult to form the identical pattern in the pigment film and the phosphor film. Thus, in the case of the patterning by only one exposure, it is desirable that the two contradicting properties, namely, the dissolving property and the development property, be satisfied at the same time, and therefore this method involves a limited condition for work. As a result, phosphor layers with color filters, which have a uniform quality, cannot be obtained.